1. Field of the Invention
Embodiments of the present invention generally relate to a process and processing chamber that are useful for improving gap-fill during an integrated circuit processing sequence.
2. Description of the Related Art
As semiconductor device geometries continue to decrease in size, providing more devices per unit area on a fabricated substrate has become increasingly important. These devices are initially isolated from each other as they are formed on the substrate, and they are subsequently interconnected to create the specific circuit configurations desired. For example, spacing between devices such as conductive lines or traces on a patterned substrate may be separated by 0.18 μm, leaving recesses or gaps of a comparable size.
Dielectric layers are used in various applications including shallow trench isolation (STI) dielectric for isolating devices and interlayer dielectric (ILD) formed between metal wiring layers or prior to a metallization process. In some cases, STI is used for isolating devices having feature dimensions as small as under about 0.5 μm. For example, a nonconductive layer of dielectric material, such as silicon dioxide (SiO2), is typically deposited over the features to fill the aforementioned gaps (gap-fill) and insulate the features from other features of the integrated circuit in adjacent layers or from adjacent features in the same layer.
In some of these cases, the aspect ratio of the depth to width of the trench to be filled exceeds 6:1. Careful control of ion and radical density is necessary for high aspect ratio features as well as for advanced active species energy specification for selective applications (for example, selective nitridation of Si vs. SiO2). During deposition, charged species tend to result in a directional flux hence resulting in bottom-up fill, while uncharged species such as radicals tend to contribute more to the deposition on the sidewall. Therefore, careful control of the ratio of ions and radicals is important. Too many radicals may grow on the sidewall and top corner of the trench and result in pinch-off of the feature. Because some sources result in better side deposition and others result in better bottom deposition, conformality has typically been achieved by using one tool for bottom fill and another tool for side fill. Minimizing the flux of radicals will allow much higher aspect ratios to be filled. Maximizing the flux of radicals will augment deposition on the sidewalls of an aspect feature. Therefore, there is need for a method of tuning and/or controlling a substrate deposition process to adequately fill features of a desired size within the one processing tool.
Ion and radical generation in all current plasma growth and deposition technologies (e.g., inductively coupled, capacitively coupled, and microwave generated plasmas) are coupled or linked because both species are created by their interaction with ions and electrons that are generated in a plasma formed in a processing region of a processing chamber. Due to the inherent broad energy distribution found in these conventional ion and radical formation techniques, the formed species have widely differing amounts of energy and a relatively fixed or skewed ratio of formed radicals to formed ions. As illustrated in FIG. 2, a typical energy distribution of an electron generated in a plasma includes a high energy initial peak at low energies (e.g., ˜2 eV) and an exponential decay in the number of electrons that have higher energies. Typically, only small changes in the ratio of ion to radical species can be made by adjusting process conditions such as pressure and gas composition. Additionally, delivery of the different types of active species can only be tuned by making major hardware changes in the processing chamber such as adding an ion filter, a remote plasma, or changing the showerhead. However, true separation of ion and radical species can generally not be accomplished using these conventional plasma processing methods. Therefore, there is a need for an apparatus and method of better controlling the radical to ion ratio without having to alter process conditions (such as pressure and gas composition) or chamber configuration during processing.